Both download endpoints (invoice/proforma) put the stored file_name raw into the Content-Disposition header. HTTP headers are latin-1, so any non-ASCII name (i.e. every Persian filename) raised UnicodeEncodeError before the body was sent -> HTTP 500. Uploads were unaffected.
Content-Disposition is now built by a helper following RFC 6266 / RFC 5987: the UTF-8 name is percent-encoded in filename*=UTF-8''..., with a header-safe ASCII fallback in filename= (quotes and control characters stripped; a name that folds away entirely becomes attachment<ext>).
Verified locally after reproducing the exact production error (same latin-1 positions 22-27): Persian proforma + invoice downloads 500 -> 200 with filename*= carrying the full Persian name and bytes sha256-matching the MinIO object; ASCII filename regression 200; helper edge cases (CRLF/quote injection stripped, empty name -> attachment, pure-Persian png -> attachment.png); no UnicodeEncodeError in the api logs after the fix.
whqreza
ali_mohaghegh